I've been gone for quite a while, but would love to have a sweetheart pet. Can someone direct me to where I can learn about the sweetheart variation?

Welcome back! You can use a to make a Sweetheart pet. These are all the ones that exist so far. You can also redeem 100 Candy Hearts at the L'amour Parlor for the potion. The link is in Other Currencies under Seasonal Currencies and Candy Hearts.

thank you very much :D